The present invention relates to a bi-directional fluid pressure-operated displacement unit, of the type including a rotary valve member, and more particularly, to an improved valve-seating mechanism for use therein.
Although the present invention may be used in various pump and motor configurations in which fluid flows axially through a valve member and contact must be maintained between the valve member and a corresponding port plate which communicates with the volume chambers of a fluid displacement mechanism, it is especially advantageous when used in disc-valve gerotor motors. Therefore, the present invention will be discussed in connection with disc-valve gerotor motors without intending to limit the scope of the invention.
Fluid motors of the type utilizing a gerotor displacement mechanism to convert fluid pressure into a rotary output are widely used in a variety of low speed, high torque commercial applications. Typically, in fluid motors of this type, the gerotor mechanism includes a fixed internally toothed member (ring) and an externally toothed member (star) which is eccentrically disposed within the ring and orbits and rotates relative thereto. In fluid motors of this type there are normally two relatively moveable valve members. One of the valve members is stationary and provides a plurality of fluid passages, each one being in permanent communication with one of the volume chambers defined by the gerotor mechanism, while the other valve member rotates relative to the stationary valve member, in commutating fluid communication therewith, as is now well known to those skilled in the low speed, high torque gerotor motor art.
Low speed, high torque gerotor motors are illustrated in U.S. Pat. Nos. 3,572,983 and 4,390,329, both of which are assigned to the assignee of the present invention and incorporated herein by reference. Fluid motors made in accordance with the cited patents include, in addition to the previously mentioned stationary valve member and rotatable disc-valve member, a valve-seating mechanism which is now also generally well known in the gerotor motor art. The general function of the valve-seating mechanism is to exert a circumferentially uniform biasing force, biasing the rotatable valve member into sliding, sealing engagement with the stationary valve member.
One of the problems with fluid motors of the disc-valve type is a condition referred to as “internal leakage.” Internal leakage is defined as a volume of fluid communicated between the high-pressure side and the low-pressure side that effectively bypasses the gerotor displacement mechanism. Since such internal leakage effectively bypasses the gerotor displacement mechanism, such leakage reduces the volumetric efficiency of the fluid motor. As is well known to those skilled in the art, internal leakage in a fluid motor varies proportionally to the operating pressure of the fluid. Therefore, as the operating pressure of the inlet fluid increases, the internal leakage in the fluid motor also increases.
A recent trend in commercial applications which use fluid motors of the disc-valve type is to require increased operating pressure ratings in the fluid motor. In addition to this requirement, the manufacturers of commercial products for those applications have requested improved volumetric efficiencies at these higher operating pressures. However, as previously stated, higher operating pressures result in more internal leakage in the fluid motor and lower volumetric efficiencies. Therefore, in order to meet these requests and requirements, it is necessary to identify, and reduce the effect of any sources of volumetric inefficiency in the fluid motor.
One location in fluid motors of the disc-valve type where internal leakage is prevalent, especially at high operating fluid pressures, is at the interface between the rotatable valve member and the valve-seating mechanism. At this location, fluid inlet, fluid outlet, and case fluid pressure forces act on the valve-confronting surface of the valve-seating mechanism and cause the valve-seating mechanism to “distort”(or deform or deflect). Such distortion, is referred to by those skilled in the art as “potato chipping.” Potato chipping occurs when the outer periphery of the valve-seating mechanism distorts, deforms or deflects more or less than the inner diameter of the valve-seating mechanism, such that the valve-confronting surface and the adjacent surface of the stationary valve member are no longer in a planar, face-to-face relationship. Distortion of the valve-seating mechanism results in a loss of sealing engagement between the valve-seating mechanism and the rotatable valve member. Internal leakage occurs at the location of this loss of sealing engagement. At higher operating pressures, this distortion, deformation or deflection is more pronounced.
In the disc-valve fluid motor art, there are two primary types of rotatable valve members. The first type is referred to as a “blind-bore” type. In the blind-bore type of disc-valve, as illustrated in the above incorporated U.S. Pat. Nos. 3,572,983 and 4,390,329, the internal cavity, in which internal splines are formed, of the rotatable valve member does not continue along the entire axial length of the valve member, and thus, fluid cannot flow axially throughout the axial length of the valve. The second type is referred to as a “thru-bore” type. In the thru-bore type of disc-valve, an internal bore, in which internal splines are formed, extends the entire axial length of the rotatable valve member. While the present invention can be used with both types of rotatable valve members, it is especially advantageous when used with a motor of the thru-bore type, and will be described in connection therewith, without intending to limit the scope of the invention.